README.rdoc

Active Model – model interfaces for Rails

Active Model provides a known set of interfaces for usage in model classes.
They allow for Action Pack helpers to interact with non-Active Record
models, for example. Active Model also helps with building custom ORMs for
use outside of the Rails framework.

Prior to Rails 3.0, if a plugin or gem developer wanted to have an object
interact with Action Pack helpers, it was required to either copy chunks of
code from Rails, or monkey patch entire helpers to make them handle objects
that did not exactly conform to the Active Record interface. This would
result in code duplication and fragile applications that broke on upgrades.
Active Model solves this by defining an explicit API. You can read more
about the API in ActiveModel::Lint::Tests.

Active Model provides a default module that implements the basic API
required to integrate with Action Pack out of the box:
ActiveModel::Model.